Certain elastomeric articles, ie. gaskets, valves and seats used in aerosol containers, are designed as part of the container for the efficacious delivery of pharmaceutically active compounds, ie. medicaments. As a matter of cost and convenience, such articles are derived using elastomeric materials such as elastomeric rubber and the like, specifically formulated with ingredients that enable the article to meet numerous demanding toxicological, chemical, and physical requirements. For example, gaskets and valves made of rubber are typically formulated with about six to twelve ingredients, including monomers, polymers, organic solvents, organic plasticizers, antioxidants, antiozonants, curing agents, accelerators, pigments, tackifiers, reinforcing materials and inorganic fillers such as carbon black. Nearly all cured or finished articles will inherently contain small amounts of residual components derived from these ingredients. These inherent residual components or impurities are not neccessary for performance of the article but can potentially interact with the medicament or other excipients in the formulation, leading to reduced pharmaceutical dosing. Such impurities could also interact with the container, causing it to malfunction, such as by blocking a nozzle orifice.
A paper by A. Figazette et al., Analysis for Extractables From Nitrile Rubber Components in Metered Dose Inhalers, Pharmaceutical Analysis Department, SmithKline Beecham Pharmaceuticals, King of Prussia, Pa., was presented at the Symposium, "Regulatory Issues in Aerosol Drug Development", Jun. 12-14, 1991 in Arlington Va. by the University of Kentucky College of Pharmacy. Figazette et al stated that contamination of pharmaceutical aerosols by substances leached from elastomeric valve assemblies in metered dose inhalers is a potentially serious problem. The authors present evidence that numerous extractables could be detected in valves from various suppliers, demonstrating a need for cleaner valve rubbers with fewer leachable extractants. One class of impurities is known as the polynuclear aromatic hydrocarbons (PNAs or PAHs). Another class of impurities is known as non-PAHs, including phthalates derived from plasticizers employed during processing. Presently, conventional methods for removing PAHs and non-PAHs from rubber articles involve liquid-solid extraction and refluxing using either conventional solvents or fluorocarbon type solvents (eg. freons). However, these conventional methods are deemed unsatisfactory for preparing purified elastomeric articles using the newer, environmentally safer fluorohydrocarbons propellants such as HFC-134A, HFC-226a and HFC-227, for the following reasons. First, these conventional methods have the disadvantage of incurring high expenses for special handling and safety precautions, and for special buildings, rooms and equipment due to the explosive nature of the newer propellants, necessitating the need to use explosion-proof equipment. Second, these conventional methods have the further disadvantage of superficially cleaning primarily the outer surface of the article, leaving impurities in the interior of the article. French patent publication 2638098 describes particulate or powder materials using supercritical fluid extraction, using solvents such as carbon dioxide. Such particulates and powders can subsequently be converted into a finished article. This reference fails to teach the purification of elastomeric articles, but rather of powders and particulates, using supercritical fluids.
Clearly, it would be desirable to provide an improved method for cleaning elastomeric articles by removal of the impurities contained therein, particularly for highly demanding pharmaceutical and medicinal uses. It would also be desirable to provide a method for preparing such articles which would meet govenmental regulatory requirements (ie. Food and Drug Administration). Furthermore, it would also be desirable to provide a method for cleaning elastomeric articles that is occupationally and environmentally safer, simpler, more rapid and less expensive than known conventional methods.